1. Field of the Invention
The invention relates in general to an element packaging structure, and more particularly to a package structure of semiconductor light emitting element.
2. Description of the Related Art
The light emitting diode (LED) emits a light by converting electricity into photo energy. The light emitting diode is mainly formed by a semiconductor. The light emitting diode, having the features of long lifespan, low temperature and high utilization rate of energy, has been widely used in various lamps and has gradually replaced conventional light sources.
Conventional surface mount technology (SMT) light emitting diode is electrically connected to an external wire substrate through at least a metal wire, such that the semiconductor layer inside the light emitting diode is electrified by the current transmitted through the metal wire to illuminate. The metal wire is commonly formed by gold which has high ductility. The metal wire is not permeable to the light and is very expensive. Considering the cost and optical transmittance, the diameter of the metal wire cannot be too large otherwise the overall light output might be affected. Also, if the differences between the coefficient of thermal expansion (CTE) of the metal wire and those of the light emitting diode and the substrate are too large, the metal wire soldered between the light emitting diode and the substrate by a wire-bonding machine may be pulled and break or the solder ball at the end of the metal wire may come off. Particularly, during the temperature cycling test, the thermal stress may affect the structural strength of the metal wire and may even cause the metal wire to break or come off and end up with an increase in product failure rate.